If you have played LittleBigPlanet then you may know what i am talking about but for those who don't heres what it is:
Say you wanted to make a horror server and wanted to make everything black and white but not just the bricks the whole environment in monochrome or an old west film in sepia. There could also be some colours for brightly lit coves and beaches or some bright reds, greens and blues for some other interesting affects.
What I think it should have:
-Monochrome and Sepia options.
-Multiple colours.
-Darker and brighter colours.
-An option to make your selection brighter or darker (Ex: a dark, monochrome world)
Don't know if it's possible for the engine but it would be pretty neat and would make builds have alot more atmosphere.